Granular ammonium nitrate and process of making same



Jan. 4, 1927. 1,613,334

E. M. SYMMES GRANULAR AMMONIUM NITRATE AND PROCESS OF MAKING SAME Filed Nov. 8, 1924 HEATER Patented Jan. 4, 1927.

UNITED STATES PATENT OFFICE.

ERNEST M. SYMMES, OF WILMINGTON, DELAWARE, ASSIGNOR TO HERCD'LES POWDER COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE.

GRANULAR AMMONIUM NITRATE 'AND PROCESS OF MAKING SAME.

Application filed November 8, 1924. Serial No. 748,548.

In the process of preparing granular ammonium nitrate, the principal use of which is as an ingredient of explosives, it'is ens-- tomary to prepare weak solutions of the salt and evaporate the solution to a certain concentration at a certain temperature, after which the solution is discharged into a graining kettle and slowly crystallized with agitation and cooling at a certain rate. The rate of crystallization and concentration of the evaporated solution controls the fineness of the product. Slow crystallization of a highly concentrated solution produces coarse particles in the form of irregular botryoidal solid crystals. Crystallizing at an increased rate results in relatively fine particles, which are also in the form of solid crystals.

Granular ammonium nitrate produced by this process is composed of solid grains, has greater density and hygroscopicity than is desirable, and when passing through the transition point at 32 C. (89.6 F.),'there is considerable external expansion.

The process forming the subject-matter of this application involves a substantially different method of treating the evaporated solution and 'efiects a substantial saving in the cost of manufacture. The resultant product has essential advantages, as compared with the ordinary granular ammoni m nitrate which may be enumerated as follows: (1) It has a lower density, thereby allowing a higher cartridge count when the salt is used as an ingredient of explosives. (2) Explosives containing the'improved ammonium nitrate have a higher sensitiveness. (3) The improved ammonium nitrate has lower hygroscopicity. (4) When passing through the transition point at 32 C. (89.6 E), there is substantially less external expansion. The external expansion of ordinary ammonium nitrate constitutes a serious objection to explosives containing ammonium nitrate in substantial proportion, as this causes the explosive to set (harden), so that it becomes relatively insensitive and may not detonate properly. The reduced setting tendency of the improved product is a quality of much importance.

The improved product is distinguished by certain physical characteristics from the ammonium nitrate that is made in the ordinary to the physical character of the ammonium I nitrate granules. Such hollow sphericahparticles cannot be manufactured by the process 111 general use, namely, the crystallization in graming kettles with agitation and cooling.

The process hereinafter described, which constitutes the preferred way of making the improved product, comprises the projection of an evaporated solution of ammonium nitrate, or molten ammonium nitrate, through a nozzle or atomizer, at a substantially 'definite pressure, into a gaseous cooling medium. Ari-apparatus adapted to carry out the process is shown in the accompanying drawing, which is a longitudinal' sectional view. of such apparatus.

It should be understood, however, that no novelty is claimed for any element of the apparatus and that the process is not dependent for its execution upon the employment of the apparatus illustrated or other particular apparatus. I

A weak neutral ammonium nitrate liquor is concentrated in the evaporator a. From the evaporator the more or less concentrated solution, by means of a pump 6, is conveyed through a steam-jacketed pipe 0 and discharged through a nozzle (i into the spray chamber e under suflicient pressure to effect the atomization of the solution. It should be understood that the term atomization is used in its popular sense to imply a division of the solution into a number of very fine particles, which will solidify be of any fore they have traversed the height of the spray chamber. The spray chamber is of substantial dimensions and is provided with a sloping bottom communicating with a hopper f, which discharges the material into a rotating drying chamber 9. From the drying cylinder the dried material is discharged, say, onto a screen It; the grains which it is desired to utilize as an explosive ingredient passing through the screen into a receiver 71, while the tailings pass overinto a separate receiver j. By means of a heater'lc and a blower m, a current of hot air or other gas is forced through the drier,

- of concentration. The degree of atomization the air thence escaping through the hopper 7 into the spray chamber e. I

The character of the material produced by the improved process is controlled by the conditions under which the process is carried out. It has been found that the density of the material varies in a substantially d1- rect ratio to the freezing point of the solution sprayed and in a substantially inverse ratio to the temperature of the solution and degree of atomization. In other-words, the density of the product resulting from spraying a solution having a freezing oint only slightly below the temperature 0% the solution when sprayed will be higher than that of the product from a solution having the same freezing, point but s rayed at a higher temperature. By contro ling the freezing point and temperature of the solution and the degree of atomization, the character of the product ma be controlled. The freezing point of the so ution varies with the degree may be varied by varying the pressure at the nozzle and to some extent by varying the I temperature of the solution when sprayed.

' in chamber As an illustration of the process, a weak solution of ammonium nitrate is concentrated in the evaporator. a to a point where the solution has a temperature of 310 F.

and at which the ammonium nitrate if taken out would freeze or crystallize at 280 F. With a steam pressure of fiftypounds to the square inch on the jacketed feed pipe 0, the solution is delivered through the pump to the nozzle (1 at a pressure of twenty pounds to the square inch. The heated air f may be at any desired temperature say 100 F. to 150 F. and is substantia ly devoid of moisture. his air,

however, is very cold relatively to the m coming spray of ammonium nitrate, and almost immediately coolsthe sprayed particles to the point of. solidification. It will be understood that there is a continuous current of dry air flowing into the bottom of chamber e and out the ventilators 0 at the top thereof. The ammonium nitrate is prolectedm the form of avast number of particles of spherical form. From contact with the cooling gaseous medium filling the spray chamber,

these s heresquickly form an exterior solidified siiell. The interior of each article freezes more slowly and, due to t e contraction that takes place on cooling, a void space is left in the. interior. The product has an apparent density of about .70 and a fineness (with the freezing point, temperature and degreeof atomization specified asan example) such that ninety-five per cent will pass through a ten mesh screen and be held on a forty mesh screen.- By increasing the atomlzin action, finer particles are produced. or example, the degree of fineness may be such that not more than five per cent will be held-on a fort mesh screen, while five per cent or more wi 1 pass through a hundred mesh screen. Whatever the de ree of fineness, the grains have a spherical form with an interior void space. Besides being much less dense than granular ammonium nitrate produced by the ordinary method, they are less hygroscopic and show less increase in volume when passing through the 32 C. transition point.

The size and density of the material are both affected by, and may be controlled by regulating,'the freezing point, temperature and degree of atomization of the liquid when sprayed. In all cases, however, the density will be low as compared with the ordinary product and there will be a close approximation to uniformity in size. The density can be easily varied from .6 to .9.

The spraying of substances in a liquid condition into a space within which they are acted on by a gaseous medium and are converted to the form of fine solid particles has been effected in apparati of various constructions. Certain of such apparati may be adapted to the execution of the present process, which, as hereinbefore stated, is not dependent on the use of any particular apparatus -nor on an apparatus which necessarily embodies any patentably novel features.

While the weak solution is described as being concentrated to a point where the solution has a temperature of 310 F., crystallizing-at 280 K, it is contemplated that these temperatures shall be subject to variation, dependent on the character or quality that it is. desired to impart to the ultimate product. It is impracticable, however, to carry the temperature of evaporation or crystallization much higher than 310 F., as decomposition occurs inthe nei hborhood of 320 F. The lowest practicable crystalliz ing temperature would be 250 F. or higher. The temperature of the gas entering the spray chamber is immaterial so long as it is substantially below the temperature of the li uid as it is'being atomized. The gas shoul of course, be nearly free from moisture. All required conditions can be satisfied by using air as the gaseous cooling medium and heating it to above F. and below 150 F.

Examples of explosives in which the improved ammonium nitrate may bev advantageously employed are as follows:

An ammonia permissible explosible having the following typical composition:

Percent. Nitroglycerin, nitropolyglycerin, nitrosugar, nitroglycol, or any other similar Ammonia dynamite (the examfplelgiven being a low freezing dynamite o so-called strength) Per cent.

Any of the above specified liquid eitp osives 1 Nitroaromatic compounds 3 Sodium nitrate 41 Carbonaceous material a 11 Ammonium nitrate Per cent. Ammonia gelatin (the example given being low freezing) Any of the above specified liquid explosives 29 Nitrocotton 0.6 Sodium nitrate 46.4 Sulphur 3.0 Carbonaceous material 15.0

Ammonium nitrate 6.0

Where in the claims, use the term concentrated to include any solution of ammonium nitrate that 'is not sohighly concentrated .that it will not flow and that is sufliciently concentrated to enable the particles thereof thatare sprayed into the spra chamberto quick- 1y solidify under the in uence of a gaseous cooling medium. The temperature of such a solution is necessarily above 240 or 250 F and referably not far from 310 F. and

much ,a ove the temperature of air that is heated only to the degree requiredto substantially-eliminate moisture therefrom.

I have not herein claimed anexplosive comprising my improved ammonium nitrate,

as the same forms the sub'ect-matter of aseparate ap lication, filed Serial No. 48,549.

Havir g now fully described my invention,

ovember 8, 1924,

fluid ammonium nitrate I mean internal cavities.

. On this 5th what I claim and desire to protect' by Letters Patent is: r

1. The rocess of making granular am- I monium mtrate which comprises conveying ammonium nitrate having a temperature above 240 F. and below 320 F. to, and 7 s raying it into, a gaseous cooling medium,

t ereby suddenly cooling the ammonium "nitrate and converting it .mto granules having an internal void space.

2. The process of making granular am-.

' monium mtrate which comprises 0011061111307 ing by evaporation a relatively weak solution of ammonium nitrate to a temperature below 320 F. and above 250 F. and sprayaway from the locus of spraying an solidification, sub'ectin the particles, while being so conveye to t e action of a flowing current of dry as, and conveying such gas to the locus o spraying and solidification, where it functions as the gaseousc'ooling medium above specified.

4. A low density ammonium nitrate comprising granules each having an internal void space.

5. Ammonium nitrate in granular form, the grains being substantially spherical with 6. Ammonium nitrate in the form of substantially spherical hollow grains and hav ingna density between .6 and .9.

testimony of which invention, I have hereunto set my hand, at Wilmington, Del.,

day of November, 1924. a

ERNEST M. SYMMES; 

